The controversy surrounding Orexigen TherapeuticsOREX-0.20% and its release of interim study data for its Contrave diet pill is quickly escalating. Amid accusations the drug maker misled investors and patients about the safety of its drug, Orexigen is now feuding withTakeda Pharmaceutical4502.TO+0.91%, its marketing partner, over the cost of a clinical trial that was required by the FDA at the time the diet drug was approved last fall.

In a statement last night, Takeda accused Orexigen of a “material breach” of a collaboration agreement that was inked five years ago and initiated a formal dispute resolution process. In its own statement, Orexigen says Takeda wants it to pay the entire cost of the trial. “We are currently evaluating the assertions made by Takeda and believe they are without merit,” Orexigen said in its statement.

The disclosure is causing Orexigen shares to drop, since the cost of the trial is estimated to be about $200 million, according to RBC Capital Markets analyst Simos Simeonidis, who calculates that Orexigen would be on the hook for as much as an extra $100 million if it loses the dispute. “Chances of that are very difficult to handicap,” he wrote in an investor note. We asked Takeda for comment and will pass along any reply.

The dispute between the drug makers follows a series of highly unusual events surrounding a safety study for the Contrave drug. Known as LIGHT, the study was designed to assess the cardiovascular risk of the pill and the FDA agreed to use interim data for regulatory approval. The drug, in fact, was approved by the agency last fall and the trial was expected to be completed in 2017.

But the FDA also learned that Orexigen violated an agreement with an executive steering committee, which was overseeing the trial, by sharing some data with more than a small coterie of employees. This prompted the agency to question the ability of the agency to rely on the final outcome of the study and required Orexigen to start a second trial that would also assess cardiovascular risks.

Yesterday, though, the executive steering committee halted the LIGHT trial, citing yet another data disclosure by Orexigen. Two months ago, the drug maker filed information about Contrave patents with the U.S. Securities and Exchange Commission and included interim data from the first study that indicated its drug lowered the risk of a heart attack, stroke or death by 41%.

That disclosure buoyed Orexigen investors, who believed Contrave would become widely prescribed. But the disclosure angered the steering committee and worried the FDA, because the final LIGHT study results could yield a different outcome. In fact, the steering committee yesterday released updated interim data showing the drug did not lower cardiovascular risk.

The steering committee decided to end the LIGHT study over concerns that doctors may increase prescribing of the drug based on unreliable safety information. Orexigen “inappropriately” compromised and “poisoned” the trial, according to Steve Nissen, the committee chair who heads cardiovascular care at Cleveland Clinic. He also told Forbes that the drug maker misled patients and investors.

His remarks angered Orexigen chief executive Michael Narachi, who told RBC’s Simeonidis that he “adamantly refutes the assertions that the company misled investors and patients.” He also maintained there was a data access plan in place, and that it was followed and included provisions for filing patents, according to the investor note. Orexigen has maintained the patent filings were material information.

Moreover, Narachi insists that Orexigen had notified the FDA in advance of its intent to include patent information with its SEC filing this part March. “The filing of the patent that unblinded the study was not a surprise to anyone,” he told RBC. We asked the FDA for comment and will update you accordingly.

So what’s next? Simeonidis notes that Orexigen disclosed that talks were already under way with Takeda to renegotiate their deal, but had been unable to reach agreement. However, he points out that Takeda could just walk away if the drug maker really wanted to do so. One plus for Orexigen is that the drug maker will not have to spend another $30 million to $40 million to complete the LIGHT trial.